Magnetic core



Jan. 1963 K. D. BEARDSLEY Em. 3,074,038

MAGNETIC CORE Filed Oct. 10, 1958 fizl'm org Kezznsf D Beards/5y, Edmund J VW/K,

3,674,038 MAGNETE'C 69% Kenneth D. Beardsley, Dalton, and Edmund J. Willi, Adams, Mass, assignors to General Electric Company, a corporation of New York Filed Oct. It), 1958, Ser. No. 766,438 4 Claims. ((3,336-213) This invention relates to a packet magnetic core and a method of making the same. More particularly, the invention is an improvement over the packet magnetic core and method of making the same described and claimed in copending Treanor patent applications Serial Numbers 712,135 and 392,205, now Patent No. 3,025,483 and Patent No. 2,960,756, respectively, which are assigned to the same assignee as the instant patent application. By the term packet core is meant one which has a plurality of radially nested curved laminations or turns which are cut into segments with a plurality or bundle of segments of the core being simultaneously laced through the opening of a preformed electrical coil assembly.

While the specification. concludes with claims particularly pointing out and distinctly claiming the subject matter which we regard as our invention, it is believed the invention will be better understood from the follow ing description taken in connection with the accompanying drawing in which:

FIG. 1 is an elevation view of a magnetic core constructed in accordance with one form of our invention, and

FIG. 2 is an exploded perspective View of the outer packet and two turn segment of FIG. 1.

The magnetic core illustrated in the drawing comprises a plurality of radially nested packets 1 to 4. The turns or laminations of the packets are spirally arranged and are cut into segments having a length of approximately one turn of the core. Preferably, the joints lti (see FIG. 2) of all the packets are arranged on the side of the core which will be positioned in the opening of a not shown preformed electrical coil. This is so as to minimize distortion of the laminations of the core when they are being laced with an electrical coil. In the particular embodiment of the invention illustrated in the drawing the segments of the packets have a length of slightly more than one turn of the core. However, as will be obvious to those skilled in the art and as is more particularly explained in the copending Treanor patent applications, the segments could have a length slightly less than one full turn of the core. Successive layer joints which are indicated by X marks in FIG. 1 are offset with respect to each other and the layer joints are distributed along the length of the left-hand side of the core so that the joint It? in each packet is relatively long with respect to its thickness. A packet joint which is relatively long with respect to its thickness is not absolutely necessary but is preferred so that the disturbance of fiux in one layer will not eiiect the disturbance of flux in an adjacent layer and also to facilitate simultaneous lacing of the cut segments of each packet with a preformed electrical coil with minimum distortion of the laminations.

In our invention adjacent packets are separated by laminations 5 to 7 which have a length of approximately two turns of the core. Also, the innermost and outermost segments 8 and 9 of the core have a length of approximately two turns of the core. Prior art magnetic cores which utilize packets do not have such extra length segments between packets and on the inside and outside of the core. The special segments provide several advantages.

In our invention additional structural strength is pro- 3,074,li38 Patented Jan. 15, 1963 vided in the core inasmuch as the two turn segments hold the core together. Additionally, the amount of looseness in the core is no longer critical inasmuch as the packet joints are held snugly closed by the two turn pieces even in an excessively loose core. The two turn inner piece 8 which defines the space or window opening in the core holds in the insulation on the not shown electrical coil assembly and thereby provides a good base on which to build the core. A two turn piece over each packet holds its joints closed whereas a clamping band or the like on the outside of the core would not accomplish this in the inner packets. Additionally, during lacing of the packets without the two turn segments there is a danger of dislodging the joints in previously laced packets. This is avoided when each packet is held closed by a two turn piece.

The preferred method of making the magnetic core is to take a strip of preferably grain oriented core material and wind it continuously into a plurality of radially superimposed turns on a generally rectangular shape mandrel. Winding the core strip on a rectangular shape mandrel gives them the configuration desired in the final core. After the desired number of turns are wound on the mandrel the turns are clamped, banded or otherwise held closed and the mandrel along with the wound core is placed in an annealing oven to give the turns a perma nent set and relieve the stresses which were introduced therein during the winding operation. After the anneal the core and mandrel are separated and then the annealed core is cut preferably from the inside to the outside. The core could be cut by unwinding it from the outside and cutting it from the outside to the inside. However, this means that the whole core must be out before any of the segments can be laced. If the core is cut from the inside to the outside then the packets can be laced with a preformed electrical coil without waiting until the whole core has been out. After the inner segment 8 is cut it can be laced with the electrical coil. As the segments of the first packet 1 are out they are set aside in a radially nested bundle. When all the segments of the first packet l are out then the packet can be opened and laced with an electrical coil. Thereafter the next two turn segment 5 is laced with the electrical coil to hold the joints of the first packet 1 closed. This procedure is continued until all the packets and segments of the core are laced with the electrical coil and the last packet and whole core is finally closed by the last two turn segment 9. In our invention the single turn segments of the packets do not necessarily have to be set aside and then laced as a group but each single turn segment could be individually laced with the core right after it has been cut. However, even with such a procedure the two turn segments still provide the afore mentioned advantages. Additionally, if the core has a very small window opening which provides insufiicient space for the cutting tool to operate on the core from the inside to the outside, the rectangular shaped core can be expanded into say an octagon which will provide more working space inside the core for the cutting tool. However, even with such an arrangement the extra length segments between packets and on the inside and outside of the core still provides the heretofore discussed advan tages of our invention.

It will be obvious to those skilled in the art that the special segments between packets and on the inside and outside of the core do not necessarily have to have a length of two turns of the core but can be somewhat shorter or longer than two turns of the core. For instance, the extra length segments could have a length of 1 /2 turns of the core and the joints in successive packets could be located on opposite sides of the core. The important thing to be considered in selecting the exact length of the special segments is that they be long enough to accomplish the purposes and advantages heretofore set forth. They could be more than two turns long. However, it is preferred not to make them too long since long segments are more difficult to assemble with the electrical winding than short segments. Therefore, by the term about two turns long is meant segments which are somewhat shorter or longer than two turns long which will satisfy the above set forth requirements.

While there has been shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and therefore, it is intended by the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In a closed magnetic core which has a window opening and a plurality of radially superposed laminations which extend continuously for about a single turn of said core, said single turn laminations being separated into groups which are held closed by laminations which are positioned between said groups and which extend continuously for about two turns of said core. 7

2. In a closed magnetic core which has a window opening and a plurality of radially superposed laminations which extend continuously for about a single turn of said core, said core having joints therein whose length is long with respect to their thickness, said joints comprising a series of butt joints in said laminations which are staggered along said first mentioned joints and progress radially outward, said series of butt joints and their respective laminations being held closed by laminations which extend continuously for about two turns of said core and are positioned between said series of butt joints.

3. A curved magnetic core comprising radially nested groups of spirally arranged approximately single turn length larninations which are butt jointed end to end, and each of said groups and said core being held closed by spiral laminations which are about two turns long and are positioned along the inside and outside of each of said groups and said core.

4. A closed magnetic core which has a window opening and radially nested groups of spirally arranged laminations which are divided into butt jointed segments having a length of approximately one turn of said core, each of said groups and their butt jointed segments being held closed by spiral laminations which have a length of approximately two turns of said core and which are alternated with said groups.

References Cited in the file of this patent UNITED STATES PATENTS 2,431,128 Link Nov. 18, 1947 2,486,220 Somerville Oct. 25, 1949 2,489,625 Dornbush Nov. 29, 1949 2,548,628 Somerville Apr. 10, 1951 2,603,691 DEntremont July 15, 1952 2,931,993 Dornbush Apr. 5, 1960 2,960,756 Treanor Nov. 22, 1960 FOREIGN PATENTS 113,740 Australia Aug. 21, 1941 

1. IN A CLOSED MAGNETIC CORE WHICH HAS A WINDOW OPENING AND A PLURALITY OF RADIALLY SUPERPOSED LAMINATIONS WHICH EXTEND CONTINUOUSLY FOR ABOUT A SINGLE TURN OF SAID CORE, SAID SINGLE TURN LAMINATIONS BEING SEPARATED INTO GROUPS WHICH ARE HELD CLOSED BY LAMINATIONS WHICH ARE 